Free-Standing PEO/LiTFSI/LAGP Composite Electrolyte Membranes for Applications to Flexible Solid-State Lithium-Based Batteries

Battery research has recently diverged into solid-state chemistry and flexible features to address the increasing demands in electric vehicles and novel electronics. In this study, we successfully fabricate 4-inch sized thin freestanding lithium-ion conducting composite electrolyte membrane. The solid electrolytes are made up of polyethylene oxide (PEO) lithiated with lithium bis(trifluoromethylsulphonyl)imide (LiTFSI) in which submicrometer sized crystalline Li1.4Al0.4Ge1.6(PO4)3 (LAGP) particles are homogeneously distributed. The impacts of the LAGP loading (20–60 wt%) on the thermal, electrical, and mechanical properties of the composite electrolytes are systematically assessed. The composite membranes exhibit similar conducting behavior of dry polymer electrolytes with two distinct ionic conduction mechanisms transitioned around the melting temperature. The conductivities of the composites are marginally lower than the polymer electrolyte with no LAGP. Addition of LAGP, compared with PEO/LiTFSI, has slightly increased thermal transition temperatures (both glass transition temperature and melting temperature) as well as the crystallinity of PEO. Increasing the amount of LAGP ceramic fillers increased the elastic modulus, reduced the strain to failure point, but has less impacts on the yielding strength. The freestanding ceramic/polymer composite electrolytes with optimal LAGP loading can result appropriate electrical, thermal and mechanical properties and hence, have potential applications to flexible all solid-state lithium-based batteries.